Jaime was riding his bike with an 11-year-old friend when a car struck the boys, causing them to fall from their bikes and run, said another sister, Alejandra Alvarado.

"They got scared and they started running," she said.

At that moment, someone got out of the car and fired a shot at Jaime, she added.

The boy was shot in the back just before 9 p.m. in the 2600 block of West 37th Place in Brighton Park, police said, citing early reports.

A witness told police the boys were surrounded by multiple vehicles and a fight ensued, said Officer Michael Sullivan, a Chicago police spokesman, citing preliminary reports. The witness heard gunshots, and then found the victim behind a vehicle, unresponsive, Sullivan said.

Alejandra Alvarado said she thinks the gunman may have been associated with a gang and perhaps mistook Jaime for someone else. Jaime was not part of a gang and was looking forward to his family's planned move from Brighton Park to the North Side in two weeks, she said.

He was also set to graduate from eighth grade in June from the Calmeca Academy of Fine Arts and Dual Language, Rocio Alvarado added.

Jaime's teacher, Concepcion Calderon, said the teen was popular among students and found a way to smile "even in hard situations." She said he told her he wanted to be a chef who would teach young people how to eat a healthy diet.

"I don't think there was one person in this school who didn't like him," Calderon said. "It was just his smile."